There have been a number of proposals to use swellable materials in oilfield applications for filling voids or blocking off water flows. Most of these are based on the use of elastomers that are capable of swelling on their own accord, as well as swellable compositions that swell after coming into contact with a material that triggers the swelling of a component of the composition. Particulate polymeric materials have also been proposed for use in cement compositions for oilfield applications.
WO2005/012686 discloses a composition comprising salt particles within a swellable elastomer; the composition swells after water penetrates into the elastomer by osmosis. US7059415 discloses a composition comprising minerals that swell on contact with water but that lose water on heating at a relatively low temperature (e.g. sodium montmorillonite) within an elastomer that swells on contact with oil.
Mineral oxides such as magnesium oxide find a number of uses in the cement and polymer industries. In the composition disclosed in U.S. Pat. No. 7,252,142, the role of magnesium oxide is to form an acido-basic cement with monopotassiumphosphate; in U.S. Pat. No. 7,247,666 magnesium oxide acts as a flame retardant in thermoplastics. U.S. Pat. No. 7,160,949 discloses inorganic fillers, which are preferably platey materials and possibly magnesium oxide, within very specific thermoplastics. Swellable clays are preferred because they can be separated into fine suspensions. Magnesium oxide may also be used as filler in rubber (U.S. Pat. No. 6,737,478), and US20070142531 discloses a cleaning blade for use in image-forming apparatus, whereby the material is an acrylonitrile-butadiene rubber and magnesium oxide is an optional filler. It has to be noted that in this document, the rubber has basically a too strong swelling capacity when subjected to toluene and thus magnesium oxide is used to diminish said capacity.
U.S. Pat. No. 7,228,915, which discloses a device and method to seal boreholes, mentions polyetheretherketone (PEEK) and other materials as a non-swelling layer on top of a swelling elastomer, and discloses that inorganic additives added to the elastomer can delay swelling.
The present invention is based on the fact that the inventors surprisingly found that swelling due to a phase change resulting from hydration of an inorganic component can provide a composition in which swelling can take place reliably even at the high temperatures encountered in borehole uses.